Liz, congratulations on working WITH your horse and not blaming him! It sounds like he is TRYING to be good for you, but overwhelmed by discomfort or too much energy. I have several suggestions. First consider his lifestyle. Grain, stall time, and time without forage are all risk factors for ulcers and behavior problems. Maximize turnout, ideally with calm companion(s). Minimize grain except to maintain weight; get a vitamin supplement instead. Free choice hay if possible.
Second, choose an instructor/trainer who helps you help your horse by focusing on your balance and communication. Your boy is probably very sensitive, so he will appreciate gentle precision. Being young and an OTTB, he may also be struggling with balance which can cause bucking and spooking. Too much focus on performance too soon can stress you both; focus on balance and communication will automatically improve performance. Finally, the more he trusts you, the better he’ll listen to you when he’s anxious. It sounds like you already have a good relationship with him; keep building on that.